This invention relates to the field of the internal combustion engines. It concerns a system for actuating a carburetor of an internal combustion engine.
Such a system is known for example from the printed document U.S. Pat. No. 4,123,480.
For the operation of motor driven hand-operated tools such as, for example, motor saws, hedge clippers, lawn mowers or the like, it is desirable to reduce the starting procedure of the engine to a few movements. Therefore, a switch position for the cold start of the engine and another switch position for starting the engine which is warm for running should be provided for. But, in order to start an engine warm for running in a first switch position, the throttle valve of the carburetor must be opened to half gas while in a second switch position for the cold start of the engine the throttle valve must be opened to half gas and the choke must be actuated. Both switch positions should return to an operating position with the acceleration of the engine. A further stop position of the switch for stopping the engine can be integrated into the switch. Such systems are known for example from DE-C2-25 09 443. For these known systems, the individual functions of the carburetor are triggered over at least one separate switch which is not associated to the carburetor and which causes the adjustment over a plurality of levers and rods.
Another carburetor system is known from the printed document mentioned in the introduction. Here, the throttle valve and the choke or the choke valve are directly coupled on the carburetor over a coupling mechanism. This coupling mechanism causes the lock of the throttle valve in the half gas position when the choke valve is closed. The choke valve is operated over a lever mechanism from outside the carburetor. However, with this solution, it is disadvantageous that for adjusting the warm start position (FIG. 4) the choke valve must first be closed and then opened again so that the respective operating position of the carburetor cannot be clearly recognized by the position of the switch for the choke adjustment.
In all, the known carburetor actuating systems have the disadvantage that the individual functions cannot be realized or can only be insufficiently realized according to the switch position. The reason of these functional defects is to be found in particular in too high tolerances in the individual levers.
Thus, the aim of the invention is to create an actuating system for a carburetor for which the individual functions xe2x80x9cready for operationxe2x80x9d, xe2x80x9cwarm startxe2x80x9dand xe2x80x9ccold startxe2x80x9dare realized in one switch, whereby the individual functions are indicated by the different position of the switch. Here, it should be assured that the individual switch positions also guarantee the corresponding carburetor functions and do not cause functional defects because of too high tolerances.
The heart of the invention consists in performing the adjustment of the carburetor with a switch directly placed on the carburetor and influencing the choke and in effecting the corresponding shifting of the throttle valve through a corresponding mechanical coupling between the choke and the throttle valve on the carburetor. Thus, a clear correspondence between the switch position and the adjustment of the carburetor is achieved. Simultaneously, lever mechanisms which are subject to tolerance are reduced to a minimum. Preferably, the choke has a choke shaft and the switch is placed directly on the choke shaft.
A preferred configuration of the invention is characterized in that the coupling means comprise a snap-in plate which is caught by the switch against the force of a spring when turning the switch from a starting position into one direction, that the coupling means further comprise a notch lever which is connected with the throttle valve and which determines the position of the throttle valve and that the snap-in plate is configured in such a way that the notch lever snaps into the snap-in plate when turning the switch from the starting position into two different positions of the snap-in plate or of the choke and holds the snap-in plate, whereby the one snap-in position of the snap-in plate corresponds to the opened choke and the other one to the closed choke and the throttle valve is in both cases in half gas position. A precise and safe coupling between the choke and the throttle valve is thus achieved in a simple way.
The automatic return movement preferably ensues in that the lock between the snap-in plate and the notch lever is configured in such a way that by adjusting the throttle valve the lock is lifted by opening the throttle and the switch with the snap-in plate returns into its starting position under the action of the spring.
Another preferred configuration of the system according to the invention is characterized in that the switch can be turned into another position in which the ignition of the engine is prevented. In this way, all necessary operating positions can be set on the carburetor with a sole switch in an uniquely recognizable way.
Further features of the invention will be apparent from the following.